Out-of-bounds Read in Zchunk
CVE-2026-117556
zchunk before 1.5.5 contains a heap out-of-bounds read vulnerability in read_preface() in src/lib/header.c that passes the total header length instead of remaining bytes to compint parsing functions. Attackers can supply a crafted .zck file whose header ends inside a compressed integer, causing reads past the heap header buffer and crashing the application.
Vulnerability class: Buffer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
Weakness classification (CWE)
References
- github.com/zchunk/zchunk/issues/119 (issue-tracking)
- github.com/zchunk/zchunk (product)
- github.com/zchunk/zchunk/commit/02b371a64bf98245df97315d07c684a0ca5ea1df (patch)
- github.com/zchunk/zchunk/releases/tag/1.5.5 (release-notes)
- github.com/zchunk/zchunk/blob/1.5.4/src/lib/header.c (technical-description)
- www.vulncheck.com/advisories/zchunk-before-1.5.5-heap-out-of-bounds-read-via-re… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-117556?
- CVE-2026-117556 is a medium-severity vulnerability in Zchunk, classified under Out-of-bounds Read. CVSS score: 4.3/10. Published 2026-10-27.
- How severe is CVE-2026-117556?
- Medium severity. CVSS v3 base score is 4.3 out of 10.